GB2281189A

GB2281189A - A safety belt pre-tensioner

Info

Publication number: GB2281189A
Application number: GB9316607A
Authority: GB
Inventors: Ralf Glaessner; Lars Axelsson
Original assignee: Autoliv Development AB
Current assignee: Autoliv Development AB
Priority date: 1993-08-10
Filing date: 1993-08-10
Publication date: 1995-03-01
Anticipated expiration: 2013-08-10
Also published as: GB2281189B; GB9316607D0

Abstract

A pre-tensioner for a safety belt in a motor vehicle comprises tension-applying means (e.g. a compression spring 12, a gas cylinder or a pyrotechnic charge) accommodated within an elongate housing 1. The pre-tensioner is normally held in the inoperative condition and incorporates a triggering arrangement 13 for activating the pre-tensioner in a accident situation. The triggering arrangement includes a locking element (14, Fig. 3) retained by balls 21, and an inertia mass (25, Fig. 2) which moves in a predetermined manner to release the balls when the vehicle in which the pre-tensioner is mounted is subjected to excessive deceleration. The inertia mass is mounted co-axially with respect to the elongate housing so as to provide for a compact construction which in turn facilitates installation in positions where space is limited. <IMAGE>

Description

DESCRIPTION OF INVENTION "A SAFETY BELT PRE-TENSIONER" THE PRESENT INVENTION relates to a safety belt pre tens loner.

It is not uncommon nowadays for a safety belt in a motor vehicle to be provided with a pre-tensioner which applies tension to the safety belt in the event of an accident. This type of pre-tensioner comprises means to apply tension to the safety belt and means to initiate operation of the device in the event of an accident. The tension applying means may act upon a buckle connected to the belt or may act upon a reel onto which the safety belt is wound, with tension being applied to the safety belt via the buckle or the reel. Alternatively the tension applying means may act to move part of the belt in a direction substantially perpendicular to the longitudinal axis of the belt, thereby tensioning the belt.

There are now various designs of pre-tensioners.

DE-OS 39 30 980 shows common arrangements of pre-tensioner, which have a spring 10 which serves to apply tension to a cable 48 which is attached to a safety belt buckle or a safety belt reel so as to apply tension to the safety belt.

The spring 10 is accommodated within a cylindrical housing 11 with one end of the spring engaging the housing and the other end engaging a piston 12 provided within the housing.

The spring 10 is normally held in a compressed state by means of a lever 14, one end of which is normally in engagement with the piston 12 in order to retain the piston in a predetermined position within the cylindrical housing, this position of the piston corresponding to the compressed state of the spring 10. The lever 14 is connected to a triggering arrangement which may take various forms.

The triggering arrangements shown in Figures 7C and 7D of DE-OS 39 30 980 each comprise an inertia mass 33, part of which engages one end of the lever 14 through the intermediary of a ball or roller 31, the other end of the lever engaging the piston 12 as mentioned above. The lever 14 is pivotally mounted and is arranged such that when the inertia mass 33 moves in response to excessive deceleration of the vehicle in which the pre-tensioner is mounted, the ball or roller 31 is moved away from the end of the lever 14 so that the lever is free to pivot and thereby release the piston 12. The piston and the cable 48 to which it is attached are then moved axially within the housing 11 under the action of the spring 10, the movement of the cable 48 exerting tension upon the safety belt to which it is connected. It will be appreciated that the triggering arrangements shown in DE-OS 39 30 980 are all disposed to one side of the housing 11 which accommodates the spring 10 and overall the pre-tensioner takes up a not insignificant amount of space.

In the region where the pre-tensioner would normally be installed in a motor vehicle space is often very limited and difficulties may well be encountered in trying to mount an arrangement such as is shown in Figure 7C or Figure 7D of DE-OS 3930 980 in the motor vehicle.

Attempts to provide a more compact triggering arrangement for the pre-tensioner have tended to result in more complex devices which are usually difficult, and therefore costly, to assemble.

The present invention seeks to provide a relatively compact pre-tensioner which is of simple design and may be easily assembled.

According to the present invention there is provided a pre-tensioner for applying tension to a safety belt in a motor vehicle, the pre-tensioner comprising means for applying tension to the safety belt, said means being accommodated within an elongate housing having a central longitudinal axis, means for retaining the tensioning means in an inoperative condition and a triggering arrangement operable in response to a predetermined deceleration of a vehicle in which the pre-tensioner is mounted for releasing the retaining means such that the tensioning means move from said inoperative condition and apply tension to the safety belt, the triggering arrangement comprising an inertia mass, the inertia mass being separate from the tensioning means and being adapted to move in a predetermined manner when subjected to said predetermined deceleration, movement of the inertia mass serving to release the retaining means, the inertia mass being mounted co-axially with respect to the elongate housing for the tensioning means.

Preferably the inertia mass is of cylindrical form and surrounds the central longitudinal axis of the elongate housing.

Conveniently the tensioning means comprise force storing means and force transmitting means for transmitting a force exerted by the force storing means to the safety belt, the retaining means comprising a component mounted on or forming part of the force transmitting means and a blocking element which engages said component and prevents movement of the force transmitting means under the action of the force exerted by the force storing means, the blocking element being mounted co-axially with respect to the elongate housing.

Advantageously the blocking element comprises a plurality of resilient fingers extending substantially axially with respect to the elongate housing, each of the fingers being fixed with respect to the housing at one end and being movable in a direction substantially perpendicular to the central axis of the housing at its other end.

Preferably said component mounted on or forming part of the force transmitting means acts to bias the free end of each resilient finger outwardly away from the central axis of the housing.

Conveniently the blocking element is mounted such that at least part thereof is located internally of the inertia mass, the free end of each resilient finger of the blocking element normally engaging the inertia mass when the pre-tensioner is "primed", the engagement of the free end of each resilient finger with the inertia mass acting to limit movement of the free end of each resilient finger under the biasing action of the component mounted on or forming part of the force transmitting means.

Advantageously the free end of each resilient finger of the blocking element engages the inertia mass through the intermediary of a ball.

In one arrangement the component mounted on or forming part of the force transmitting means comprises a leaf spring, the leaf spring having a plurality of arms, a respective arm engaging each of the resilient fingers of the blocking element and urging it outwardly away from the central axis of the housing.

In an alternative arrangement an inclined surface is defined on the component mounted on or forming part of the force transmitting means or is formed on the free end of each resilient finger of the blocking element, the component mounted on or forming part of the force transmitting means engaging the free ends of the resilient fingers of the blocking element via said inclined surface which causes the free ends of the resilient fingers of the blocking element to be urged outwardly away from the central axis of the housing under the action of the tensioning means.

In this alternative arrangement both the component mounted on or forming part of the force transmitting means and the free end of each resilient finger of the blocking element may define co-operating inclined surfaces.

In addition to the urging of the free ends of the resilient fingers of the blocking element outwardly away from the central axis of the housing via an inclined surface, a spring may be provided on the blocking element, the spring urging all of the resilient fingers of the blocking element outwardly away from the central axis of the housing.

Preferably the tensioning means comprise a compression spring, one end of which engages a fixed part of the housing.

In order that the present invention may be more readily understood and so that further features thereof may be appreciated the invention will now be described by way of example with reference to the accompanying drawings in which: Figure 1 is a partly sectioned elevation of a pretensioner in accordance with the present invention, with an upper portion of a triggering arrangement for the pretensioner shown in the locking position and a lower portion of the triggering arrangement shown in the release position in which the pre-tensioner has been activated.

Figure 2 is an enlarged, partly sectioned elevation showing the triggering arrangement of Figure 1, again with an upper portion shown in the locking position and, a lower portion shown in the release position, in which the pretensioner has been activated; Figure 3 is an enlarged, perspective view of one component of the triggering arrangement for the pretensioner; Figure 4 is an end elevation of a spring component of the pre-tensioner; and Figure 5 is a view corresponding to Figure 2 but showing a slightly modified embodiment of the triggering arrangement for the pre-tensioner.

Referring initially to Figures 1 and 2 of the accompanying drawings a pre-tensioner comprises a substantially tubular elongate housing 1 which accommodates all of the components of the pre-tensioner, the housing 1 having a central, longitudinal axis 2. The pre-tensioner is designed to apply tension to a safety belt in an emergency situation by means of a cable or wire 3, one end of which is connected to the safety belt either via a buckle to which the belt is connected in use or via a reel upon which the belt is wound. The cable 3 passes around a guide wheel 4 mounted in an enlarged end region 5 of the housing 1 and extends to a head 6 connected to one end of a rod 7. The rod 7 extends along the central axis 2 of the housing 1 and carries a cap or plunger 8 at its opposite end.

At a position adjacent the enlarged end region 5, the housing 1 is formed with an inwardly directed annular flange 9 to which a cylindrical tube 10 is fixed, the tube 10 extending co-axially within the housing 1 on one side of the flange 9. The tube 10 terminates at a position spaced from the free end of the rod 7 which extends inside the tube 10 and projects beyond the free end thereof. Adjacent its free end the tube 10 is formed with an indentation 11, the purpose of which will be explained hereinafter. A helical compression spring 12 surrounds the tube 10, the opposite ends of the spring 12 engaging the flange 9 of the housing 1 and the end cap or plunger 8 located at the free end of the rod 7. It will be appreciate that when the spring 12 is compressed it will apply a force urging the cap or plunger 8 to the left in Figure 1, which in turn results in tension being applied to the cable 3. Thus the spring 12 forms the tensioning means by way of which tension is applied to a safety belt, via the cable 3, in an accident situation.

The pre-tensioner is, of course, normally held in a inoperative condition and incorporates a triggering arrangement, generally identified by reference numeral 13 which serves to activate the pre-tensioner when a motor vehicle in which it is fitted is subjected to a deceleration in excess of a predetermined limit.

The triggering arrangement 13 is disposed on the opposite side of the flange 9 of the housing 1 to the spring 12 and is best illustrated in Figure 2 of the drawings.

The triggering arrangement comprises a central blocking element 14 which is shown in perspective view in Figure 3 of the drawings. The blocking element comprises a ring 15 which is fixed in position adjacent the inwardly directed surface of the annular flange 9 of the housing so as to be seated against the free end of the tube 10, as can be seen in Figure 1. Thus, the ring 15 cannot move to the left as seen in Figure 1 of the drawings. Six resilient fingers 16 extend from the surfaces of the ring 15 which is opposite the surface in engagement with the free end of the tube 10, the fingers 16 extending axially of the housing 1 but not quite parallel to the longitudinal axis 2 thereof.

At the point where each finger 16 is joined with the ring 15, a recess or groove 17 is formed in th finger so that it is joined to the ring 15 by a relatively thin web of material which permits the fingers 16 to flex or move in a radial direction with respect to the cylindrical housing 1. It will be appreciated that the blocking element 14 effectively "surrounds" the central longitudinal axis 2 of the housing 1 and is therefore co-axial with the housing and with the spring 12. At its free end each of the resilient fingers terminates with a stepped portion 18, a step 19 being defined on the radially inwardly directed surface of each finger at its free end. The radially outwardly directed surface of the free end of each finger defines a groove or recess 20 within which a ball 21 is seated, as will be described in greater detail hereinafter.

A spider-like leaf spring 22 is mounted beneath the head 6 on the cable 3, the leaf spring comprising a central annular portion 23 and six equiangularly spaced radially outwardly directed spokes 24 (see Figure 4). The spokes 24 are angled with respect to the central annular portion of the spring, so that an included angle of approximately 120C is defined between each of the spokes 24 and the central annular portion 23, as can be seen in Figure 2 of the drawings. Each spoke 24 of the leaf spring 22 engages in a respective step 19 on one of the resilient fingers 16 and urges its associated finger 16 radially outwardly, the spokes being compressed radially inwardly upon assembly of the triggering arrangement.

The triggering arrangement further comprises an inertia mass 25 which is of cylindrical form and which surrounds the blocking element 14 and is therefore coaxial with respect to the housing 1 and the spring 12. The inertia mass 25 is acted upon at one end by a biasing spring 26 which biases the inertia mass to the right in Figures 1 and 2 of the drawings. One end of the biasing spring 26 is accommodated within a groove formed in the cylindrical inertia mass 25 whilst the other end of the biasing spring is seated within a small groove formed in the annular flange 9 of the housing 1. The right hand end of the cylindrical inertia mass 25 is counterbored such that an internal rim or step 27 is defined. This rim acts as a seat for the balls 21 which are each also seated within a groove 20 in a respective finger 16 of the blocking element 14.

The triggering arrangement shown in Figure 2 is designed and assembled such that the balls 21 are normally held in position between the free ends of the fingers 16 and the end of the inertia mass 25 with the leaf spring 22 urging the free ends of the fingers 16 radially outwardly so as to press the balls 21 into the rim or stop 27 defined by the inertia mass and with the spring 26 biasing the inertia mass to the right in Figures 1 and 2 thereby pressing the balls 21 into the grooves 20 formed at the free end of each finger 16. Thus, the depth of the grooves 20 and the angle of the spokes 24 of the leaf spring 22 are, of course, designed so that the balls 21 will normally be held captive in the manner shown in the top half of Figure 2 and will not be urged out from between the fingers 16 and the inertia mass 25 by the forces acting upon them, when the pre-tensioner is inoperative. It will of course be appreciated that the upper portion of Figure 2, that is to say the portion above the central axis 2 illustrates the triggering arrangement when in the normal position where the pre-tensioner is "primed" but not activated. The lower portion of Figure 2 below the central axis 2 illustrates the triggering arrangement when the pre-tensioner is activated and will now be described in further detail.

The pre-tensioner is mounted in a motor vehicle with the left hand end of the housing 1, as seen in Figure 1, directed towards the front of the vehicle. The vehicle will therefore normally be moving towards the left, as indicated by the arrow 28 in Figure 2. If the vehicle is subjected to a sudden deceleration, such as arises in an accident situation, the inertia mass 25 will continue moving to the left under its own inertia whilst the housing 1 which is fixed to the chassis of the vehicle will be rapidly decelerated. The blocking element 14, which is connected to the housing 1 by its engagement with the free end of the tube 10 and the flange 9 of the housing, will therefore also be rapidly decelerated.

The movement of the inertia mass 25 relative to the blocking element 14, against the action of the biasing spring 26, will serve to release the balls 21 from their captive positions between the inertia mass 25 and the fingers 16 of the blocking element, as is shown in the lower portion of Figure 2 of the drawings. It will be recalled that the spokes 24 of the leaf spring 22 act to urge the free ends of the fingers 16 radially outwardly and, once the inertia mass 25 has moved slightly to the left the spokes 24 force the free ends of the resilient fingers 16 radially outwardly and thereby assist in forcibly ejecting the balls 21 from their normal captive positions, as can be seen in the lower portion of Figure 2.

It is to be borne in mind that the main tensioning spring 12 is constantly acting upon the plunger 8 and attempting to tension the cable 3 and draw the cable to the left as seen in Figure 2. Normally the engagement of the spokes 24 with the steps 19 formed in the free ends of the resilient fingers 16 prevents the main spring 12 from drawing the cable to the left, but once the resilient fingers 16 move radially outwardly upon release of the balls 21 the internal angle between the spokes 24 and the annular portion 23 of the leaf spring 22 increases and the engagement of the spokes 24 with the steps 19 can no longer act to prevent the spring 12 from drawing the cable 3 to the left. Thus the leaf spring 22 is initially moved to a flattened condition, as shown in solid line in the bottom half of Figure 2 of the drawings when the cable 3 has been drawn slightly to the left. Continued movement of the cable 3 to the left under the action of the spring 12 causes the spokes 24 of the leaf spring 22 to be bent backwards whereupon the spokes will be pulled along the internal surfaces of the resilient fingers 16 in the manner as is shown in dotted lines and identified by the reference numeral 24' in the bottom half of Figure 2.

The pre-tensioner is provided with a non-return mechanism 29 (shown in Figure 1) which is of a conventional design and well known to those skilled in the art, the nonreturn mechanism serving to retain the cable 3 in the tensioned condition when the pre-tensioner has been activated. The non-return mechanism comprises an element mounted within the tube 10, the component defining a space or chamber which accommodates a series of balls which engage the internal surface of the tube 10. The balls will roll along the internal surface of the tube 10 when the pre-tensioner is activated but will be forced tightly into engagement with the internal surface of the tube 10 by rising up an inclined surface and will grip the internal surface of the tube and prevent any movement of the cable 3 to the right in Figure 1 of the drawings. The indentation 11 formed in the tube 10 adjacent its free end acts as a stop which engages the main component of the nonreturn mechanism 29 when the pre-tensioner is activated.

Figure 5 illustrates a slightly modified embodiment of the triggering arrangement 13. In this modified arrangement the leaf spring 22 which forms the connection between the cable 3 and the central blocking element 14 has been replaced by an alternative arrangement for urging the free ends of the resilient fingers 16 radially outwardly and for preventing axial movement of the cable 3 under normal conditions.

In one modified arrangement the leaf spring 22 may be omitted and the head 6 mounted on the cable 3 may directly engage the free end of each resilient finger 16, the head 6 and the end of each finger 16 being formed with sloping or chamfered surfaces, as shown generally by reference numeral 30 in Figure 5, these sloping surfaces resulting in the head 6 urging the fingers 16 radially outwardly as a result of the axial force exerted upon the head 6 by the main spring 12. It is, of course, possible that a sloping surface on the head 6 alone would be perfectly adequate or that a sloping surface on the free end of each resilient finger alone would be adequate. If necessary an additional spring element 31 could be provided in order to urge the resilient fingers 16 radially outwardly, the spring element 31 taking the form of a horseshoe-shaped or near-circular spring which is compressed upon being inserted in position in grooves formed in the inwardly directly surfaces of the resilient fingers 16 and thereby acting to urge the fingers radially outwardly.

This modified embodiment works in very much the same way as the previously described embodiment. Thus, in an accident situation the inertia mass 25 will move to the left and the balls 21 will be released from their normally captive positions and the resilient fingers 16 will move radially outwardly thereby freeing the head 6 so that the head and the cable 3 to which it is connected are pulled to the left under the action of the main spring 12 thereby tensioning the cable and the safety belt to which the cable is connected.

It will be appreciated from the above description that the triggering arrangement 13 is co-axial with the main housing 1 and the tensioning means, i.e. the spring 12. In particular the inertia mass 25 is a cylindrical component which surrounds the central longitudinal axis 2 of the housing. Similarly the central blocking element 14 is mounted symmetrically around the central longitudinal axis 2 of the housing. This makes for a very compact construction with both the tensioning means and the trigger therefor being arranged in a linear manner. This compact arrangement is particularly beneficial when mounting the pre-tensioner in a motor vehicle where space for mounting the pre-tensioner is limited. In addition it will be appreciated that the triggering arrangement is of a relatively simple construction comprising the sensor mass and its biasing spring, the central blocking element 14, the balls 21 and the leaf spring which extends between the cable 3 and the central blocking element. This simple construction is relatively easy to assemble and this helps to keep production costs down. Thus the pre-tensioner arrangements described above are fairly compact whilst being easy to assemble.

It will be appreciated that various modifications may be made to the specific embodiments described above without departing from the scope of the present invention.

For example, whilst a compression spring 12 has been shown as the tensioning means, a gas cylinder, a pyrotechnic charge or some other means could readily constitute the tensioning means.

Claims

CLAIMS:

1. A pre-tensioner for applying tension to a safety belt in a motor vehicle, the pre-tensioner comprising means for applying tension to the safety belt, said means being accommodated within an elongate housing having a central longitudinal axis, means for retaining the tensioning means in an inoperative condition and a triggering arrangement operable in response to a predetermined deceleration of a vehicle in which the pre-tensioner is mounted for releasing the retaining means such that the tensioning means move from said inoperative condition and apply tension to the safety belt, the triggering arrangement comprising an inertia mass, the inertia mass being separate from the tensioning means and being adapted to move in a predetermined manner when subjected to said predetermined deceleration, movement of the inertia mass serving to release the retaining means, the inertia mass being mounted co-axially with respect to the elongate housing for the tensioning means.

2. A pre-tensioner according to Claim 1 wherein the inertia mass is of cylindrical form and surrounds the central longitudinal axis of the elongate housing.

3. A pre-tensioner according to Claim 1 or Claim 2 wherein the tensioning means comprise force storing means and force transmitting means for transmitting a force exerted by the force storing means to the safety belt, the retaining means comprising a component mounted on or forming part of the force transmitting means and a blocking element which engages said component and prevents movement of the force transmitting means under the action of the force exerted by the force storing means, the blocking element being mounted co-axially with respect to the elongate housing.

4. A pre-tensioner according to Claim 3 wherein the blocking element comprises a plurality of resilient fingers extending substantially axially with respect to the elongate housing, each of the fingers being fixed with respect to the housing at one end and being movable in a direction substantially perpendicular to the central axis of the housing at its other end.

5. A pre-tensioner according to Claim 4 wherein said component mounted on or forming part of the force transmitting means acts to bias the free end of each resilient finger outwardly away from the central axis of the housing.

6. A pre-tensioner according to Claim 5 wherein the blocking element is mounted such that at least part thereof is located internally of the inertia mass, the free end of each resilient finger of the blocking element normally engaging the inertia mass when the pre-tensioner is "primed", the engagement of the free end of each resilient finger with the inertia mass acting to limit movement of the free end of each resilient finger under the biasing action of the component mounted on or forming part of the force transmitting means.

7. A pre-tensioner according to Claim 6 wherein the free end of each resilient finger of the blocking element engages the inertia mass through the intermediary of a ball.

8. A pre-tensioner according to any one of Claims 5 to 7 wherein the component mounted on or forming part of the force transmitting means comprises a leaf spring, the leaf spring having a plurality of arms, a respective arm engaging each of the resilient fingers of the blocking element and urging it outwardly away from the central axis of the housing.

9. A pre-tensioner according to any one of Claims 5 to 7 wherein an inclined surface is defined on the component mounted on or forming part of the force transmitting means or is formed on the free end of each resilient finger of the blocking element, the component mounted on or forming part of the force transmitting means engaging the free ends of the resilient fingers of the blocking element via said inclined surface which causes the free ends of the resilient fingers of the blocking element to be urged outwardly away from the central axis of the housing under the action of the tensioning means.

10. A pre-tensioner according to Claim 9 wherein both the component mounted on or forming part of the force transmitting means and the free end of each resilient finger of the blocking element define co-operating inclined surfaces.

11. A pre-tensioner according to Claim 9 or Claim 10 wherein in addition to the urging of the free ends of the resilient fingers of the blocking element radially outwardly away from the central axis of the housing via an inclined surface, a spring is provided on the blocking element, the spring urging all of the resilient fingers of the blocking element outwardly away from the central axis of the housing.

12. A pre-tensioner according to any one of the preceding claims wherein the tensioning means comprise a compression spring, one end of which engages a fixed part of the housing.

13. A pre-tensioner substantially as herein described with reference to and as shown in Figures 1 to 4 of the accompanying drawings.

14. A pre-tensioner substantially as herein described with reference to and a shown in Figures 1 and 3 of the accompanying drawings when modified in accordance with Figure 5.

15. Any novel feature or combination of features disclosed herein.